install/55498: HP Compaq NC6120 hard reset shortly after mountroot, even in single user mode in NetBSD 9.0 or above

[matt%croughan.sh@localhost]

>Number:         55498
>Category:       install
>Synopsis:       HP Compaq NC6120 hard reset shortly after mountroot, even in single user mode in NetBSD 9.0 or above
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    install-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Jul 19 05:30:01 +0000 2020
>Originator:     Matthew Croughan
>Release:        NetBSD-9.0
>Organization:
N/A
>Environment:
N/A Can't boot
>Description:
HP Compaq nc6120: Intel Pentium M family 6 model 13 stepping 8 ucode 0x20

This bug occurs on any version of NetBSD above 8.2

Upon booting the installer media from USB on a HP Compaq NC6120, the machine hard resets shortly after mountroot, even in single user mode.
Using boot -vcx to enter userconf and disabe the i915drmkms driver advances the boot further, to the point that you can see the installer 'dialog' menu, but still immediately resets.

This bug occurs on the this installer media:

http://nycdn.netbsd.org/pub/NetBSD-daily/HEAD/latest/images/NetBSD-9.99.69-i386-install.img.gz

https://cdn.netbsd.org/pub/NetBSD/NetBSD-9.0/images/NetBSD-9.0-i386-install.img.gz

This bug DOES NOT occur on this installer media:

https://cdn.netbsd.org/pub/NetBSD/NetBSD-8.2/images/NetBSD-8.2-i386-install.img.gz

Below is the output of 'cat /proc/cpuinfo:'

~~~~
processor    : 0
vendor_id    : GenuineIntel
cpu family    : 6
model        : 13
model name    : Intel(R) Pentium(R) M processor 1.73GHz
stepping    : 8
microcode    : 0x20
cpu MHz        : 800.000
cache size    : 2048 KB
physical id    : 0
siblings    : 1
core id        : 0
cpu cores    : 1
apicid        : 0
initial apicid    : 0
fdiv_bug    : no
f00f_bug    : no
coma_bug    : no
fpu        : yes
fpu_exception    : yes
cpuid level    : 2
wp        : yes
flags        : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov clflush dts acpi mmx fxsr sse sse2 ss tm pbe nx bts cpuid est tm2
bugs        : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds swapgs itlb_multihit
bogomips    : 3466.87
clflush size    : 64
cache_alignment    : 64
address sizes    : 32 bits physical, 32 bits virtual
power management:
~~~~
>How-To-Repeat:
Boot installer media from a NetBSD version of 9.0 or above.
>Fix:
N/A